Semiconductor laser array device

ABSTRACT

A semiconductor laser array device comprising a substrate with a plurality of grooves and an active layer disposed over the substrate, resulting in optical waveguides within the active layer corresponding to the grooves, wherein the grooves are disposed over the entire area of the substrate and a means for preventing the injection of current into some of the grooves that are positioned outside of the central area of the substrate is disposed whereby the other grooves positioned in the central area of the substrate constitute a laser array portion of the semiconductor laser array device.

BACKGROUND OF THE INVENTION

1. Field of the invention:

This invention relates to a semiconductor laser array device withstabilized operation characteristics.

2. Description of the prior art:

With the advance of semiconductor laser devices that produce high outputpower, more attention has been paid to semiconductor laser arraydevices. For the production of semiconductor laser array devices, thereare mainly three crystal growth methods, molecular beam epitaxy (MBE),metal-organic chemical vapor deposition (MOCVD), and liquid phaseepitaxy (LPE). A semiconductor laser array device that is produced byLPE has been proposed by Matsumoto; Journal of Applied Physics, vol.58(7), P 2783-2785 (1985) in which a V-channeled substrate inner stripe(VSIS) structure with three waveguides is disclosed. FIGS. 16A to 16Cshow the production process of a semiconductor laser array device withten waveguides. On a p-GaAs substrate 301, an n-Al₀.1 Ga₀.9 As currentblocking layer 302 with a thickness of 0.7 μm and an n-GaAs protectivefilm 303 with a thickness of 0.1 μm are successively formed by LPE (FIG.16A). Then, ten grooves 320 with a width of 4 μm each, a depth of 0.9 μmeach and a pitch of 5 μm are formed by a photolithographic technique andan etching technique in such a way that they reach the substrate 301through both the current blocking layer 302 and the protective layer 303(FIG. 16B). Then, on the protective layer 303 including the grooves 320,a p-Al₀.4 Ga₀.6 As cladding layer 304 having a thickness of 0.3 μm inthe areas over the protective layer 303, an Al₀.1 Ga₀.9 As active layer305 with a thickness of 0.08 μm, an n-Al₀.4 Ga₀.6 As cladding layer 306with a thickness of 1.2 μm, and an n-GaAs contact layer 307 having athickness of 1.5 μm are successively formed by LPE (FIG. 16C). Thesemiconductor laser array device produced in this way is disadvantageousin that the grooves 320 are not completely filled with the p-claddinglayer 304, resulting in a bend of the active layer 305, which causes aweakness of the optical-coupling between the adjacent waveguides. Thus,laser oscillation occurs in the individual waveguide, which causesdifficulties in attaining laser oscillation in a synchronous phase mode.

SUMMARY OF THE INVENTION

The semiconductor laser array device of this invention, which overcomesthe above-discussed and numerous other disadvantages and deficiencies ofthe prior art, comprises a substrate with a plurality of grooves and anactive layer disposed over said substrate resulting in opticalwaveguides within said active layer corresponding to said grooves,wherein said grooves are disposed over the entire area of said substrateand a means for preventing the injection of current into some of saidgrooves that are positioned outside of the central area of saidsubstrate is disposed whereby the other grooves positioned in thecentral area of said substrate constitute a laser array portion of saidsemiconductor laser array device.

In a preferred embodiment, the grooves are disposed with a certain pitchin the waveguiding direction of laser beams.

In a preferred embodiment, at least one groove is disposed on each sideof the grooves for constituting a laser array portion positioned on thecentral area of said substrate.

In a preferred embodiment, the grooves that are positioned outside ofthe central area of said substrate are disposed at a certain angle tothe waveguiding direction of laser beams.

In a preferred embodiment, the substrate has a mesa in the central areathereof and a current blocking layer is disposed outside of said mesa,whereby the injection of current into the grooves that are positionedoutside of said mesa is prevented.

In a preferred embodiment, the means for preventing the injection ofcurrent into the grooves positioned outside of the central area of saidsubstrate is constituted by a buried structure composed of buryinglayers, a ridge guide structure composed of an insulating film, or ahigh-resistive structure composed of a proton-injected layer.

In a preferred embodiment, an impurity is diffused into the portions ofthe semiconductor layers that are positioned over the central area ofsaid substrate whereby the injection of current into the grooves thatare positioned outside of the central area of said substrate isprevented.

Thus, the invention describes herein makes possible the objectives of(1) providing a semiconductor laser array device with stabilizedoperation characteristics that has a flat and uniform active layerregardless of the number of waveguides; (2) providing a semiconductorlaser array device with a flat and uniform active layer that attainslaser oscillation in a synchronous phase mode; and (3) providing amethod for the production of a semiconductor laser array device with aflat and uniform active layer by which the semiconductor laser arraydevice is produced with reproducibility with a high yield.

BRIEF DESCRIPTION OF THE DRAWINGS

This invention may be better understood and its numerous objects andadvantages will become apparent to those skilled in the art by referenceto the accompanying drawings as follows:

FIG. 1 is a sectional view showing a semiconductor laser array device ofthis invention.

FIG. 2 is a sectional view showing another semiconductor laser arraydevice of this invention.

FIG. 3 is a sectional view showing another semiconductor laser arraydevice of this invention.

FIG. 4 is a sectional view showing another semiconductor laser arraydevice of this invention.

FIG. 5A is a sectional view showing another semiconductor laser arraydevice of this invention.

FIG. 5B is a plane view showing an arrangement of the grooves shown inFIG. 5A.

FIGS. 6A to 6F are diagrams showing a production process of thesemiconductor laser array device shown in FIG. 1.

FIGS. 7A to 7D are diagrams showing another production process of thesemiconductor laser array device shown in FIG. 1.

FIG. 8A is a sectional view showing another semiconductor laser arraydevice of this invention.

FIG. 8B is a plane view showing an arrangement of the grooves formed onthe substrate of the semiconductor laser array device shown in FIG. 8A.

FIG. 9A is a sectional view showing another semiconductor laser arraydevice of this invention.

FIG. 9B is a plane view showing an arrangement of the grooves formed onthe substrate of the semiconductor laser array device shown in FIG. 9A.

FIG. 9C is a plane view showing another arrangement of the grooves ofthe semiconductor laser array device of FIG. 9A.

FIG. 10A is a sectional view showing another semiconductor laser arraydevice of this invention.

FIG. 10B is a plane view showing an arrangement of the grooves formed onthe substrate of the semiconductor laser array device shown in FIG. 10A.

FIG. 10C is a plane view showing another arrangement of the grooves ofthe semiconductor laser array device of FIG. 10A.

FIG. 11 is a sectional view showing another semiconductor laser arraydevice of this invention.

FIGS. 12A and 12B are a diagram showing the production process ofanother semiconductor laser array device of this invention.

FIGS. 13A to 13C are a diagram showing the production process of anothersemiconductor laser array device of this invention.

FIG. 14A is a sectional view showing another semiconductor laser arraydevice of this invention.

FIG. 14B is a sectional view showing another semiconductor laser arraydevice of this invention.

FIG. 14C is a sectional view showing another semiconductor laser arraydevice of this invention.

FIGS. 15A to 15C, respectively, are plane views showing otherarrangements of the grooves formed on the substrate of the semiconductorlaser array device shown in FIG. 13C.

FIGS. 16A to 16C are a diagram showing the production process of aconventional semiconductor laser array device.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Example 1

FIG. 1 shows a semiconductor laser array device of this invention, whichcomprises a p-GaAs substrate with a mesa 1a in the central portionthereof and an n-GaAs first current blocking layer 10 disposed on bothsides of the mesa 1a. On both the mesa 1a and the n-GaAs first currentblocking layer 10, an n-Al₀.1 Ga₀.9 As second current blocking layer 2,an n-GaAs protective layer 3, a p-Al₀.4 Ga₀.6 As cladding layer 4, anAl₀.1 Ga₀.9 As active layer 5, an n-Al₀.4 Ga₀.6 As cladding layer 6, andan n-GaAs contact layer 7 are successively disposed. A plurality ofgrooves 8 exist in such a manner that they reach the p-GaAs substrate 1through the n-AlGaAs second current blocking layer 2. The grooves 8positioned in the n-GaAs first current blocking layer 10 do not reachthe p-GaAs substrate 1. Accordingly, current is injected into the activelayer 5 through the grooves 8 in the area of the mesa 1a, but theinjection of current into the active layer 5 is prevented in the area onboth sides of the mesa 1a by the n-GaAs first current blocking layer 10.

In this way, the semiconductor laser array device mentioned above isprovided with the grooves 8 over the substantially entire area of thesubstrate 1, resulting in a flat and uniform active layer 5, whichallows an occurrence of synchronous phase-coupling between the adjacentwaveguides in the active layer 5. Thus, this semiconductor laser arraydevice can attain stabilized operation characteristics.

FIGS. 6A to 6F show a production process of the above-mentionedsemiconductor laser array device. As shown in FIG. 6A, the mesa 1a witha width of 40 μm and a height of 1.0-2.0 μm is formed on the p-GaAssubstrate 1 by an etching technique. Then, as shown in FIG. 6B, then-GaAs first current blocking layer 10 is formed on the p-GaAs substrate1 in a manner to make the top surface thereof flat. Then, as shown inFIG. 6C, the entire surface area of the n-GaAs first current blockinglayer 10 is etched so as to remove the portion of the n-GaAs firstcurrent blocking layer 10 positioned over the mesa 1a, so that thesurface of the remaining current blocking layer 10 becomes flush withthe surface of the mesa 1a. The thickness of the remaining currentblocking layer 10 is 1.0 μm.

Then, as shown in FIG. 6D, on both the n-GaAs substrate 1 and the n-GaAscurrent blocking layer 10, the n-Al₀.1 Ga₀.9 As second current blockinglayer 2 with a thickness of 0.7 μm and the n-GaAs protective layer 3with a thickness of 0.1 μm are successively formed. Then, as shown inFIG. 6B, the grooves 8 with a width of 4 μm each, a depth of 1.0 μm eachand a pitch of 5 μm are formed in the substrate 1 by a photolithographictechnique and an etching technique in such a manner that the groovespositioned in the mesa 1a reach the substrate 1 through both theprotective layers 3 and the current blocking layer 2, resulting in agrating with a pitch of 5 μm on the entire surface of the substrate 1.The pitch is set so that optical-coupling between the adjacentwaveguides in the active layer 5 can be achieved.

Then, as shown in FIG. 6F, on the protective layer 3 including thegrooves 8, the p-Al₀.4 Ga₀.6 As cladding layer 4 having a thickness of0.25 μm on the protective layer 3, the Al₀.1 Ga₀.9 As active layer 5with a thickness of 0.08 μm, the n-Al₀.4 Ga₀.6 As cladding layer 6 witha thickness of 1.2 μm and the n-GaAs contact layer 7 with a thickness of1.5 μm are successively formed by LPE. Since the second current blockinglayer 2 is made of Al₀.1 Ga₀.9 As, it does not undergo meltback duringthe LPE growth process.

Since this semiconductor laser array device has the grooves 8 formedover the entire area of the substrate 1, the p-Al₀.4 Ga₀.6 As claddinglayer 4 is uniformly grown, so that the active layer 5 can be formedwith a flat surface and a uniform thickness on the said cladding layer4. Moreover, since current is injected into only the grooves 8 thatreach the p-GaAs substrate 1, laser oscillation is carried out in theportion of the active layer 5 that is positioned only over the mesa 1aof the substrate 1.

FIGS. 7A to 7D show another production process of the semiconductorlaser array device shown in FIG. 1, by which the production of the laserarray device can be simplified. The steps shown in FIGS. 7A, 7C and 7D,respectively, correspond to those of FIGS. 6A, 6E and 6F.

As shown in FIG. 7B, on the p-GaAs substrate 1 with the mesa 1a, then-GaAs first current blocking layer 10 is formed by LPE, underconditions where the top surface of the first current blocking layer 10is made flat, in such a manner that it has a thickness of 0.2 μm on themesa 1a and a thickness of 1.5 μm on the other area. Then, on the firstcurrent blocking layer 10, the n-Al₀.1 Ga₀.9 As second current blockinglayer 2 with a thickness of 0.6 μm and the n-GaAs protective layer 3with a thickness of 0.1 μm are successively formed by LPE. By this way,the total thickness W of the crystals from the first current blockinglayer 10 to the protective layer 3 that are positioned on the mesa 1abecomes 0.9 μm, and accordingly, the groove 8 with a thickness of 1.0 μmare formed so that they can reach the substrate 1. As mentioned above,the steps shown in FIGS. 6B to 6D can be replaced by the step shown inFIG. 7B, which simplifies the production process as a whole, resultingin a laser array device with a high yield.

Example 2

FIG. 2 shows another semiconductor laser array device of this inventionin which a buried structure is used as a means for preventing theinjection of current into the grooves 8 that are positioned on both sideareas of the substrate 1. This semiconductor laser array device isproduced as follows: The portions from the n-type contact layer 7 to then-type second current blocking layer 2 that are positioned on both sideareas of the substrate 1 are removed. Both side areas of the substrate 1are also removed with a certain depth. Then, the remaining areas on bothsides of the substrate 1 are filled with an n-AlGaAs first burying layer20a, a p-AlGaAs second burying layer 20b, and a p-GaAs third buryinglayer 20c in that order.

Instead of the burying layers 20a, 20b and 20c, a high-mesa structurecan be also used.

Example 3

FIG. 3 shows another semiconductor laser array device of this invention,in which a ridge guide structure is used as a means for preventing theinjection of current into the grooves that are positioned on both sideareas of the substrate 1. This semiconductor laser array device isproduced as follows: The portions of the n-type contact layer 7positioned over both side areas of the substrate 1 are removed. Then,the portions of the n-type cladding layer 6 positioned over both sideareas of the substrate 1 are also removed to a certain depth. Aninsulating film 30 of SiO₂, Si₃ N₄ or the like is formed on the exposedportions of the contact layer 7 and the cladding layer 6.

Instead of the insulating film 30, the remaining portions positionedover both side areas of the substrate may be filled with a p-AlGaAsburying layer.

Example 4

FIG. 4 shows another semiconductor laser array device of this invention,in which a proton-injected structure (i.e., a high-resistive structure)is used as a means for preventing the injection of current into thegrooves that are positioned over both side areas of the substrate 1.Protons are injected into the n-type cladding layer 6 through the n-typecontact layer 7, resulting in a proton-injected layer 40 withsemi-insulating characteristics. Boron or iodine can be also used asatoms to be injected.

Example 5

FIGS. 5A and 5B show another semiconductor laser array device of thisinvention, which is produced as follows: On an n-GaAs substrate 11, ann-Al_(x) Ga_(1-x) As cladding layer 12 with a thickness of 1.5 μm, anAl_(y) Ga_(1-y) As active layer 13 with a thickness of 0.08 μm, ap-Al_(x) Ga_(1-x) As first cladding layer 14 with a thickness of 0.2 μm,and an n- or p-GaAs light absorbing layer 15 with a thickness of 0.6 μmare successively formed by molecular beam epitaxy, organic metal-vaporphase epitaxy, or the like, wherein x<y. Then, a plurality of grooves 18with a width of 5 μm and a pitch of 6 μm are formed in the entire areaof the light absorbing layer 15 by a photolithographic technique and anetching technique in such a manner that the grooves 18 have asymmetrically branching structure as shown in FIG. 5B. The etchingprocess for the formation of the grooves 18 are carried out using anetchant containing ammonia and they reach the first cladding layer 14through the light absorbing layer 15.

Then, on both the light absorbing layer 15 and the first cladding layer14, a p-Al_(y) Ga_(1-y) As second cladding layer 16 and an n-GaAscontact layer 17 are successively formed by organic metal-vapor phaseepitaxy, so that the grooves 18 are filled with the second claddinglayer 16. Then, zinc is diffused into the center area of the grownlayers including the contact layer 17, the second cladding layer 16 andthe light absorbing layer 15 at 900° C. for two hours in which a SiO₂film is used as a mask, resulting in a p-type zinc diffusiion area 50.Since the zinc diffusion area 50 is of a p-type, current is injectedonly into the said area 50.

The waveguides in the light emitting area of this laser array device areequivalent to each other. Each of the waveguides is symmetrical withregard to the imaginable axis thereof, so that the propagationcoefficients of laser beams passing through the waveguides become equalto each other, whereby synchronous laser oscillation can be attained. Solong as the zinc diffusion area 50 acts to define the area into whichcurrent is injected, the depth of the said diffusion area 50 is notlimited to a fixed value.

Current blocking structures other than those disclosed in Examples 1-5can be used by which the same effects as metioned above are attained.Moreover, this invention is applicable to laser array devices in whichthe polarity type of the current blocking layer is the same as that ofthe cladding layer positioned in the vicinity of the said currentblocking layer, and is also applicable to laser array devices in whichthe polarity types of all lasers are different from those of the layersof the above-mentioned examples. Moreover, this invention is, of course,applicable to laser array devices of the -InGaAsP/InP system or thelike.

Example 6

FIGS. 8A and 8B show another semiconductor laser array device of thisinvention, which is produced as follows: On a p-GaAs substrate 101, ann-GaAs (or an n-GaAlAs or an n-GaAs/GaAlAs multi-layered structure)current blocking layer 102 with a thickness of 1 μm is formed by LPE.Then, as shown in FIG. 8B, a plurality of striped grooves 103 with awidth of 4 μm are formed with a pitch of 5 μm in the substrate 101 by aphotolithographic technique and an etching technique in a manner toreach the substrate 101 through the current blocking layer 102,resulting in optical waveguides. The central group 104 of the grooves103 functions as a light emitting area of the semiconductor laser arraydevice and the other groups 105 of the grooves 103 that are positionedat a distance of 6 μm from both sides of the central group 104 functionto make the active layer of the semiconductor laser array device flatand uniform. The shape and the pitch of the grooves 105 are notnecessarily the same as those of the grooves 104.

Then, on the current blocking layer 102 including the grooves 103, ap-Ga_(1-x) Al_(x) As cladding layer 106 having a thickness of 0.2 μm onthe area outside of the grooves 103, a p- (or n-) Ga_(1-y) Al_(y) As (ora GaAs/GaAlAs quantum well structure) active layer 107 with a thicknessof 0.08 μm, an n-Ga_(1-x) Al_(x) As cladding layer 108 with a thicknessof 1 μm, and an n⁺ -GaAs cap layer 109 with a thickness of 2 μm aresuccessively formed by LPE, resulting in a double-heterostructuremulti-layered crystal for laser-oscillating operation (wherein O≦y>x>1).Since there are the grooves 105 at a distance of 6 μm from both sides ofthe light emitting area (i.e., the semiconductor laser array portion)104, a uniform diffusion of As of the Ga source material solutionarises, which makes the active layer 107 flat and uniform at and in thevicinity of the laser array portion 104 when the active layer 107 isgrown on the n-type cladding layer 106.

Then, a resist film (not shown) is formed as a protective film on thelaser array portion 104 by photolithography, and protons are injectedinto the area other than the laser array portion 104 by the ioninjection method, resulting in a high-resistive area that is positionedoutside of the laser array portion 104. As a result, current flows inthe laser array portion 104, and any optical-coupling between theadjacent waveguides is not attained in the area on both sides of thesaid laser array portion 104 and moreover the injection of current intothe area on both sides of the said laser array portion 104 is prevented.

Then, a p-sided electrode 100 and an n-sided electrode 111 are formed onthe back face of the substrate 101 and the upper face of the cap layer109, respectively, the wafer is cleaved at right angles to the grooves103 so as to have a cavity length of 200-300 μm. Then, the cleaved facesare coated with a reflecting film made of Al₂ O₃ or amorphous Si by anelectron beam vapor deposition method. By changing the thickness of thereflecting film, the reflection index thereof can be set to be in therange of about 2% to 95%. To obtain a high optical output power, an Al₂O₃ film with a thickness of λ4 (λ is the oscillation wavelength) isformed on the light-emitting cleaved face, resulting in a front facetwith a reflection index of about 2%, and a multi-layered film composedof an Al₂ O₃ film and a Si film is formed on the opposite face by theelectron beam vapor deposition method, resulting in a rear facet with areflection index of about 95%.

The resulting semiconductor laser array device of this example exhibiteda threshold current of 100 mA and oscillated laser with a double peakfar-field pattern in a stabilized synchronous mode up to 200 mW opticaloutput power.

As mentioned above, by the formation of grooves 105 on both sides of thelaser array portion 104, a flat and uniform active layer 107 can bemade. Moreover, current and light can be effectively confined within thelaser array portion 104, so laser oscillation can be attained in asynchronous mode over the entire area of the laser array portion 104.

As a method by which the injected current is confined only within thelaser array portion 104, this invention is not, of course, limited tothe proton injection method. The waveguiding structure (the centralgroove structure) of the laser array portion and the groove structure onboth sides of the laser array portion are not limited to a parallelstriped-structure.

EXAMPLE 7

FIGS. 9A and 9B show another semiconductor laser array device of thisinvention in which a p-GaAs substrate 123 with a mesa 123a is used so asto confine an injected current within the laser oscillating area of thesemiconductor laser array device by the use of a current blocking layercomposed of the n-Ga₀.9 Al₀.1 As layer 121 and the n-GaAs layer 122. Thewaveguiding structure of this semiconductor laser array device isconstituted by symmetrically branching waveguides that are created inthe active layer corresponding to the symmetrically branching grooves103 as shown in FIG. 9B.

FIG. 9C shows another waveguiding structure of the above-mentionedsemiconductor laser array device that is different from that of FIG. 9Bin that the grooves 103 of FIG. 9C positioned on both sides of the laserarray portion are designed to be straight from one facet to the other,whereas the grooves 103 of FIG. 9B are curved.

EXAMPLE 8

FIGS. 10A and 10B show another semiconductor laser array device of thisinvention in which the waveguiding structure is constituted bysymmetrically branching waveguides corresponding to the symmetricallybranching grooves 103 in such a manner that the symmetrically branchingwaveguides are smoothly combined in the vicinity of both facets. Thecurrent blocking structure (the striped structure) by which current isconfined within the light-emitting area of this semiconductor laserarray device is formed as follows: The portions of the n-GaAs cap layer109 and the n-GaAlAs cladding layer 108 that are positioned outside ofthe light-emitting area are removed by an etching technique, followed byforming an insulating film 131 of SiN of the like thereon.

Another current blocking structure can be formed by the removal of theportions of the n-GaAs cap layer 109, the n-GaAlAs cladding layer 108,the active layer 107, the p-GaAlAs cladding layer 106, and the GaAssubstrate 101, by the use of an etching technique, and by thedisposition of an insulating film thereon. In this case, the grooves 103positioned on both sides of the laser array portion are finally removed.

FIG. 10C shows another waveguiding structure that is different from thatof FIG. 10B in that the waveguides positioned on both sides of the laserarray portion branch as well.

EXAMPLE 9

FIG. 11 shows another semiconductor laser array device of this inventionin which a selective diffusion technique is applied to the area of then-GaAs cap layer 109 other than the light-emitting area by the use ofZn, resulting in a p-GaAs region 141. The p-n junction obtained betweenthe p-GaAs region 141 and the n-cap and cladding layers 109 and 108gives rise to the confinement of current within the light-emitting area.

EXAMPLE 10

FIGS. 12A and 12B show the production process of another semiconductorlaser array device of this invention. A multi-layered crystal structureshown in FIG. 12A is formed by an epitaxial growth technique in the sameway as described in the above-mentioned examples. Then, the portions ofthe multi-layered crystals positioned on both sides of the laser arrayportion 104 are removed from the cap layer 109 to the substrate 101 by achemical etching technique. Then, on the remaining portions positionedon both sides of the laser array portion 104, an n-GaAlAs burying layer151, a high-resistive GaAlAs layer 152, and a p-GaAlAs burying layer 153are successively formed by a selective epitaxial growth technique,resulting in a current blocking structure. The grooves 105 positioned onboth sides of the laser array portion 104 are, as a result, removed.

Although Examples 6-10 disclose the use of an n-type substrate, a p-typesubstrate can be employed in which the other layers have differentpolarity types from the above-mentioned polarity types. Moreover, thisinvention is also applicable to InGaAsP/InP systems.

EXAMPLE 11

FIGS. 13A to 13C shows the production process of another semiconductorlaser device of this invention. On a p-GaAs substrate 201, an n-Al₀.1Ga₀.9 As first current blocking layer 202 with a thickness of 0.7 μm andan n-GaAs protective layer 203 with a thickness of 0.1 μm aresuccessively formed (FIG. 13A). Then, a plurality of grooves 220 with awidth of 4 μm, a depth of 1.0 μm and a pitch of 5 μm are formed in amanner to reach the substrate 201 through the first current blockinglayer 202 by a photolithographic technique and an etching technique. Thegrooves 220 form a laser array portion of the semiconductor laserdevice. Grooves 221 are formed at an angle of 10° or more to thewaveguiding direction of laser beams (i.e., the direction of the grooves220). When each groove 220 is positioned in the space between theadjacent mesas, each groove 221 that is formed in the space between theadjacent reversed-type mesas is disposed at right angles to the groove220 (FIG. 13B).

Then, in the same way as described in the above-mentioned examples, onthe protective layer 203 including the grooves 220 and 221, a p-Al₀.4Ga₀.6 As cladding layer 204 having a thickness of 0.25 μm outside of thegrooves, an Al₀.1 Ga₀.9 As active layer 205 with a thickness of 0.08 μm,an n-Al₀.4 Ga₀.6 As cladding layer 206 with a thickness of 1.2 μm, andan n-GaAs contact layer 207 with a thickness of 1.5 μm are successivelyformed by LPE (FIG. 13C). Since the current blocking layer 202 is madeof Al₀.1 Ga₀.9 As, it does not undergo meltback during the LPE growthprocess. Moreover, since the grooves 220 and 221 exist over the entirearea of the substrate 201, the p-type cladding layer 204 is uniformlygrown, which makes the active layer 205 flat and uniform. The activelayer 205 is neither curved nor discontinued.

Then, the portions of the n-GaAs layer 207 and the n-AlGaAs claddinglayer 206 that are positioned over the grooves 221 are removed by anetching technique, followed by coating there with an insulating film 230made of SiO₂, Si₃ N₄ or the like, resulting in a ridge guide structure(FIG. 13C) by which current is confined within the active layer 205corresponding to the laser array portion.

In the above-mentioned semiconductor laser array device, since thedirection of the grooves 221 is different from that of the grooves 220forming the laser array portion, laser beams generating from thewaveguides that are created in the active layer 205 corresponding to thegrooves 221 attain a suppressed reflection at the facets, which makeslaser oscillation difficult from the said waveguides.

Example 12

FIG. 14A shows another semiconductor laser array device of thisinvention, which is the same structure as that of Example 11 except thatthe laser array device of FIG. 14A uses a buried structure for theconfinement of current, instead of the ridge guide structure of FIG.13C. The portions from the contact layer 207 to the substrate 201 thatare positioned on both sides of the laser array portion (i.e., over thegrooves 221) are removed by an etching technique. On the remainingportions positioned on both sides of the laser array portion, ann-AlGaAs first burying layer 241, a p-AlGaAs second burying layer 242,and a p-GaAs third burying layer 243 are successively formed by anepitaxial growth technique.

Example 13

FIG. 14B shows another semiconductor laser array device of thisinvention, which is the same structure as that of Example 11 except thatthe laser array device of FIG. 14B uses a proton injected structure forthe confinement of current, instead of the ridge guide structure of FIG.13C, in which protons are injected into the areas 250 that arepositioned on both sides of the laser array portion, resulting in areaswith semi-insulating characteristics.

Example 14

FIG. 14C shows another semiconductor laser array device of thisinvention, in which by the use of a ridged substrate, current isinjected only into the grooves positioned in the central area of thesubstrate. This laser array device is produced as follows: A mesa 290 isformed on a substrate 201 by an etching technique. An n-GaAs firstcurrent blocking layer 260 is formed on the substrate 201, and the firstcurrent blocking layer 260 is etched so that the top surface of thefirst current blocking layer 260 becomes flush with the top surface ofthe mesa 290 of the substrate 201 in the same way as described inExample 1. Then, in the same way as described in Example 11, an n-Al₀.1Ga₀.9 As second current blocking layer 202 and an n-GaAs protectivelayer 203 are successively formed on both the substrate 201 and thefirst current blocking layer 260. Then, grooves 220 are formed in such amanner that they reach the substrate 201 through the second currentblocking layer 202. Grooves 221 are also formed in the same way, butthey do not reach the substrate due to the first current blocking layer260. Thereafter, layers 204 to 207 are successively formed on theprotective layer 203 including the grooves 220 and 221 in the same wayas described in Example 11, resulting in a semiconductor laser arraydevice in which current is injected only into the area corresponding tothe grooves 220 in the mesa 290 of the substrate 201. Accordingly, thelight emission of this laser array device is carried out in the areapositioned over the mesa 290 of the substrate 201.

This invention is, of course, applicable to other current-confiningstructures by which the same affects as mentioned above can be attained.

Example 15

FIGS. 15A-15C, respectively, show other arrangements of grooves of thisinvention. Grooves 221 are disposed at an angle to the grooves 220 thatform the laser array portion of the semiconductor laser array device(FIG. 15A and 15B), so that a uniform and flat active layer can begrown, which allows the semiconductor laser array device to attain laseroscillation in a stabilized mode. Grooves 221 can be also disposed inthe two or more directions different from that of the grooves 220 (FIG.15C).

With regard to Examples 11-15, this invention is most applicable to thefollowing laser array devices:

(1) devices in which the polarity type of each of the current blockinglayer 202 and the protective layer 203 is different from that of theabove-examples;

(2) devices in which the polarity type of each layer is different fromthat of the above-mentioned examples;

(3) devices in which the polarity type of each layer except for thecurrent blocking layer 202 and the protective layer 203 is differentfrom that of the above-mentioned examples;

(4) devices in which the grooves partly include symmetrically branchinggrooves; and

(5) devices in which crystal layers other than a crystal layer forfilling the grooves therewith are grown by crystal growth techniquesother than LPE.

It is understood that various other modifications will be apparent toand can be readily made by those skilled in the art without departingfrom the scope and spirit of this invention. Accordingly, it is notintended that the scope of the claims appended hereto be limited to thedescription as set forth herein, but rather that the claims be construedas encompassing all the features of patentable novelty that reside inthe present invention, including all features that would be treated asequivalents thereof by those skilled in the art to which this inventionpertains.

What is claimed is:
 1. In a semiconductor laser array device comprisinga substrate with a plurality of first grooves with a given pitch, and acurrent blocking layer with a conductivity type that is different fromthat of said substrate and that is disposed on the groove-side surfaceof said substrate, an improved structure wherein:said current blockinglayer has a plurality of second grooves on its crystal growth surfacethat is opposite to the groove-side surface of said substrate; aheterostructure multi-layered crystal is disposed on said currentblocking layer, said multi-layered crystal having an active layer forlaser oscillation; and the position of each of the first grooves isshifted half a pitch from that of each of the second grooves in acentral area elongated substantially along the laser oscillationdirection, and wherein each of the first grooves is positioned over eachof the second grooves in side areas, said second grooves reaching saidsubstrate through said current blocking layer in said central area,which results in current paths.
 2. A semiconductor laser array deviceaccording to claim 1, wherein the position of each of the first groovesin said central area is shifted half a pitch from that of each of thefirst grooves in said side areas.
 3. A semiconductor laser array deviceaccording to claim 1, wherein the position of each of the second groovesin said central area is shifted half a pitch from that of each of thesecond grooves in said side areas.